Lapping



Patented May 4, 1948 UNITED STATES PATENT OFFICE LAPPING Fred E. West, Indianapolis, Ind.

No Drawing. Application May 1, 1944, Serial No. 533,655

2 Claims. 1

This invention relates to the art of lapping and is particularly concerned with improved laps.

It is quite common to lap parts where accurate and close dimensions are required. In carrying out the lapping operation, the lap and surface to be lapped are caused to move relatively to each other. A lapping compound containing a fine, abrasive is applied to the lap or work or both and the relative movement of the lap and surface to be lapped causes metal to be removed by the abrasive action.

Laps have been made heretofore of numerous materials. In general the materials selected for this purpose are relatively soft. It has been common to form laps of gray ast iron. Gray cast iron contains a substantial amount of free carbon present in the form of flakes of graphite disposed throughout the material. In the lapping operation the free carbon acts as a lubricant and the material, because of the relatively porous character thereof, readily takes a charge of lapping compound. In addition to these characteristics, laps of gray cast iron are relatively inexpensive and are easily machined to the size and shape desired.

I have discovered that improved laps can be produced by hardening and drawing laps formed of cast iron in a manner analogous to the harde ing and drawing heat treatments employed w th steel. The cast iron lap is first heated to a suitable hardening temperature and then is rapidl cooled to harden the same. It is thereafter preferably reheated to a suitable drawing temperature. Tests indicate that the life of heat treated cast iron laps is from two to four times that of those that have not been treated.

Metallographic examination indicates a considerable change in the microstructure of the heat treated lap as compared with that of one that has not been heat treated, although there is 40 in water and thereafter reheated to a drawing temperature of 950 F. The lap before heat treatment was quite soft as indicated by a hardness of 80 Rockwell B, whereas after being hardened and 5 drawn, a hardness of 25 to 30 Rockwell C was obtained.

The foregoing example of lap composition and heat treating procedure is given by way of illustration and not of limitation. Considerable variations may be employed in the composition of the cast iron. The heat treating conditions may vary somewhat depending on the composition of the cast iron and other factors.

I claim:

1. A method of treating a lap material which includes heating to a temperature of about 1725 F. a cast iron containing about 2.85% graphitic carbon, .08% combined carbon, 2.21% silicon, .14% nickel, .ll% chromium, .197% phosphorus, and .086% sulphur, rapidly cooling the heated cast iron, and thereafter reheating the cast iron to a temperature of about 950 F.

2. A lap of hardened and drawn cast iron, said lap containing about 2.85% graphitic carbon, .08% combined carbon, 2.21% silicon, 14% nickel, .ll% chromium, 197% phosphorus, and .086% sulphur.

FRED E. WEST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 451,327 Klar Apr. 28, 1891 1,854,508 Drake Apr. 19, 1932 FOREIGN PATENTS Number Country Date 848,809 France July 31, 1939 OTHER REFERENCES Machinerys Handbook, "Laps and Lapping, 5th edition, 1918, New York Industrial vPress; pages 969-972.

Certificate of Correction Patent No. 2,441,124. May 4, 1948.

FRED E. WEST It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 2, line 26, claim 2, for

197% read 197%; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patentj Oflice.

Signed and sealed this 14th day of September, A. D. 1948.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

